This invention relates generally to relief valves in piping systems and, more particularly to a relief valve which is heat sensitive.
A substantial concern in the operation of fluid systems that may be exposed to local temperature gradients is thermal damage to system components. Exposure to heat is prevalent among fluid systems, as tubes and pipes are frequently located nearby heat-generating components of machines and industrial equipment. When heat is transferred into a pipe, fluid temperature can rise to levels that leave components served by the piping system susceptible to damage. Therefore, thermal relief valves are frequently included in fluid systems to prevent damage. When fluid temperature exceeds a predetermined limit, thermal relief valves open to vent hot fluid and permit entry of cooler fluid.
More specifically, this invention relates to an improved thermal relief valve of the type described in U.S. Pat. No. 5,641,119, which is incorporated herein by reference. In that patent, a thermal relief valve is described as suitable for conventional or miniature fluid piping systems. The thermal relief valve includes a cylindrical valve body with a bore that houses a thermal actuator. The actuator has a piston and wax that melts and expands at a predetermined temperature. When fluid temperature exceeds the predetermined level, wax expands and causes the piston to extend, thereby moving the thermal actuator axially within the housing. The actuator moves from its normal closed position in which the actuator engages an O-ring seal to an open position in which the actuator unseats from the O-ring and forms a gap therebetween. Fluid may then pass through the valve, flowing first through an annular passage between the circular exterior of the thermal actuator and the circular interior wall of the bore in the valve body that houses the actuator. The fluid next flows through the gap adjacent the O-ring seal and exits the valve.
One drawback to thermal relief valves of this type is that in use they exhibit a high susceptibility to O-ring wear. Valves are frequently exposed to environments of severe vibration. Although the thermal actuator in its closed position is constrained from moving axially, being pressed against the O-ring by a spring, the actuator is not constrained from moving laterally. Specifically, the actuator can shift and vibrate in a side-to-side direction within the housing. As it moves, the annular passage between the thermal actuator and the interior wall of the bore in the valve body becomes irregular, wider on one side than on an opposite side, since the actuator is intermittently off-center within the bore. The actuator rubs against the O-ring seal, maintaining a sealing contact against it, but causing wear on the O-ring. The eventual results are leakage and a need for recurrent O-ring replacement.